When steam is manufactured from water, its temperature remains the same as that of the water. There is a specific relationship between steam temperature and pressure under saturation conditions. As such, saturated steam can only acquire energy by removing the steam from direct contact with water and by adding more heat to the body of steam as in a boiler superheater. As an example, steam might be generated at a temperature of 600.degree. F. and a pressure of 300 psi which corresponds to about 190.degree. of superheat. A typical application at the utilization point of the steam could be a tube and shell heat exchanger which works most efficiently if most of the steam superheat is removed before it enters the exchanger so that the steam may give up its heat of condensation. If not done, the steam will simply pass through the exchanger as a gas and very little heat transfer to the exchanger tubes will take place. In such an application, residual superheat of approximately 10.degree. F. could be tolerated while other devices may tolerate higher degrees of superheat making precise temperature control easier.
A wide variety of desuperheater designs are available. Most of these cool or desuperheat steam by injecting a water spray into the steam pipe in the same direction as the steam flow. For example, Copes--Vulcan produces a number of desuperheating configurations. Perhaps the most straightforward design is a simple mechanical atomizing type desuperheater which consists of a main tube and spray nozzle. Cooling water flows through the main tube to the nozzle, which injects water droplets in the direction of steam flow in an attempt to achieve rapid absorption of the liquid water.
Another type of desuperheater consists of a steam atomizing device which includes a spray head having a series of nozzles arranged in a circle. Atomizing steam from a higher pressure source is introduced through the steam ports of the device at right angles to the radial cooling water holes thereby blasting each of the cooling water jets. The cooling water is projected at high velocity with small droplet size into the steam header where it is distributed and vaporized.
Yet another type of desuperheater is provided with a variable orifice consisting of a housing with self-regulating orifice. This orifice is made up of a circular seat with a flow plug maintained in concentric position by a plug guide. Cooling water enters the orifice chamber and is uniformly distributed around its periphery. The amount of water injected into the superheated steam is controlled by a diaphragm operated valve actuated by a temperature controller.
Generally, most prior art devices are situated in environments in which steam velocities are in the range of 30 to 300 feet per second. Nozzle spray patterns are often conical and nozzle water velocities must be high for two reasons. Firstly, one must avoid the steam momentum from collapsing the spray pattern into a central core. As such, nozzle exit velocity must be much higher than the steam velocity. Secondly, a high nozzle velocity must be maintained over the water flow rate range in order to produce small water droplets to give good contacting efficiency. As noted from the above discussion, as efficiencies improve, nozzle configurations become correspondingly more complex. Very high nozzle velocities lead to the need for stellite nozzle construction to minimize nozzle erosion. Pipe erosion can also be a problem and special linings have been employed to cope with such situations.
It is thus an object of the present invention to provide a device to improve the efficiency of desuperheaters regardless of the various environments in which such devices are located.
It is yet a further object of the present invention to provide an enhancement to desuperheaters in the form of a motionless mixing apparatus having no moving parts and is thus not complex nor subject to clogging or breakdown when used in severe environments.